As a disk drive, for example, a magnetic disk drive includes a magnetic disk disposed in a case, a spindle motor that supports and rotates the magnetic disk, and a magnetic head that reads/writes data from/to the magnetic disk. The magnetic head has a slider mounted on a suspension and a head section provided in the slider and the head section includes a recording head for writing and a reproducing head for reading.
In recent years, magnetic heads for perpendicular magnetic recording have been proposed to achieve a higher recording density, a larger capacity, or a smaller size of a magnetic disk drive. In such a magnetic head, a recording head has a main pole that generates a perpendicular magnetic field, a write shield magnetic pole arranged on a trailing side of the main pole with a write gap therebetween to close a magnetic path to a magnetic disk, and a coil to pass a magnetic flux to the main pole. Further, a high-frequency assist head that passes a current to a high-frequency oscillator, for example, a spin torque oscillator provided between a medium-side end of the write shield magnetic pole and the main pole through the main pole and the write shield magnetic pole is proposed.
In a conventional magnetic head, the quality of recorded signals is improved by shortening a distance (=write gap length) between the main pole and the write shield magnetic pole in an ABS (air bearing surface) of a head slider to increase the gradient of a magnetic field generated by the main pole and to shorten a magnetic transition width on the recording medium.
Further, in a high-frequency assist head, like a conventional magnetic head, it is absolutely necessary to make the write gap length shorter. However, magnetic coupling between the main pole and the write shield magnetic pole becomes stronger by the write gap length being made shorter and thus, a gap magnetic field increases. As a result, if an attempt is made to increase the gradient of the head magnetic field from the main pole, the frequency of a high-frequency magnetic field applied to a recording medium becomes larger than the resonance frequency of the recording medium, causing a problem of degradation of recorded signal quality.